(1) Field of Invention
This invention relates to laser diode package, in particular to the heat sink of a laser diode package.
(2) Brief Description of Related Art
In the prior art of a laser diode, the substrate is an insulator, incapable of effectively sinking the heat generated in the laser diode. FIGS. 1-3 show such a prior art laser diode package. FIG. 1 shows the top view of a surface mount package. The substrate is the insulated substrate 10 of a printed circuit board. Metal plates 11, 12, 13 serve as leads. A metal pedestal 111 is place on the metal plate 11 for mounting a laser diode. Semicircular recesses 14 are cut into the metal plates, 11, 12, 13 for inserting clamping screws onto the substrate 10.
FIG. 2 shows a laser diode 15 mounted on the pedestal 111. The laser diode 15 emits light rays B and F left and right respectively of the laser diode 15 along the section line AAxe2x80x2 as shown in FIG. 3. A photo diode 16 is mounted on the metal plate 11 for monitoring the light rays B. The light ray F is emitted from the package. The metal plate 11 serves as the lead for the bottom electrode of the laser diode 15. The top electrode of the laser diode 15 is wire bonded by wire 17 to the metal plate 12, serving as another lead for the laser diode 15. The top electrode of the photodiode 16 is wire-bonded by wire 18 to the metal plate 13.
A glue 19 is used to seal the laser diode 15 and the photo diode 16. The glue 19 covers up to the edge of the laser diode 15, leaving an open end to emit the light without attenuation. The metal plates 11, 12, 13 may each have plated through channels as shown in FIG. 3, or plated through holes (not shown) or folded plate (not shown) for easy surface mounting to a circuit board.
Such a prior art package has poor heat sinking capability, because the printed circuit substrate is a poor heat conductor. When is laser diode is energized, the heat cannot be removed effectively and may cause the laser diode to be overheated.
An object of the present invention is to provide a laser diode package, capable of heat sinking effectively the heat generated in the laser diode. Another object of the invention is to provide a laser diode package having provisions to monitor the heat generated in the laser diode. Still another object of the invention is to provide means to automatically adjust the power generated by the laser diode.
These objects are achieved in this invention by using thick metal plates serving both as leads and substrate for the laser diode. The thick metal plates serve as good heat sinks. One of the thick plates has a step. A monitoring photo diode is mounted in the lower platform of the step. A glue is used to seal the laser diode and the photo diode and to aggregate the metal plates, the laser diode and the photo diode together as a unitary structure.